1. Field of the Invention
The present invention relates to electrical resistance elements, and more particularly relates to an electrical resistance element having a heat-sensitive disconnect capability.
2. Description of the Prior Art
Conventional electrically energized, elongated heating elements currently on the market and commonly referred to as heating cords generally utilize high resistance metallic conductors, such as nichrome wires, embedded within a plastic substrate, whereby the conductors are coupled in series in order to form a complete electrical path through the element and thus generate heat. A common use for such elongated heating elements is to wrap the element around a water pipe to prevent the pipe from freezing.
One of the major problems with such commercially available heating elements is that they may produce "hot spots", for example, if they are double wrapped such that a portion of the element is wrapped over another portion. The hot spots occur at the double wrapped portions of the elongated heating element. The element may overheat and cause a fire. Usually, such resistance elements are sold with warning labels advising the consumer not to double wrap the element.
Another problem with many conventional elongated heating elements is that they have a fixed length. Those conventional elements that may be cut to a desired length require that the two nichrome wires be reconnected at the ends that are cut to form a closed circuit. This requirement is not only an annoyance but also could be dangerous when 115 volts is employed in energizing the element.
U.S. Pat. Nos. 4,758,815 and 4,823,106, each of which issued to the present inventor, Walter Lovell, the disclosures of which are incorporated herein by reference, disclose a heat generating, electrical resistance tape element. The resistance tape element basically includes a pair of flat, parallel, spaced apart ribbon conductors and an elongated strip of commercially available magnetic recording tape which at least slightly overlaps and contacts the ribbon conductors. The electrical conductors and magnetic recording tape are laminated between top and bottom plastic covering sheets. The laminated heating tape disclosed in the Lovell U.S. patents mentioned above has many advantages over conventional heating elements including its ability to be rolled up tightly for shipment, its capability of being manufactured inexpensively and its ability to be cut to a desired length without the need to connect the terminal portions together prior to use.